$\begingroup$Is this a kind of flower or fungi? I ask because if so it could be all manner of deadly flower or fungi that releases spores, like deathcap etc.$\endgroup$
– JamesMar 8 '18 at 0:40

$\begingroup$@James Hmm I believe that if it was the name of a flower it would have the knowledge tag, but I'm not sure.$\endgroup$
– NL628Mar 8 '18 at 5:15

$\begingroup$Any number of electronic components could fit this description. "Capacitor" comes to mind, since they're often referred to as "caps", and store a potentially dangerous charge.$\endgroup$
– BlueRaja - Danny PflughoeftMar 8 '18 at 12:54

$\begingroup$Is it strange that you got more answers than votes?$\endgroup$
– ChowzenMar 10 '18 at 3:40

You can touch a light bulb's "cap" (which is the glass housing around the bulb).

But if you touch my stem

The "stem" of the bulb is inside it. This is key for the next clue!

Unfriendly air will you meet.

Thanks to @Quentin, we know that this clue has to do with the inability of Noble Gases to form bonds. Argon (a Noble Gas) is a common gas found inside light bulbs, so if you're touching the stem, you're gonna meet a Noble Gas. Probably not for long, though, if the cap is off. :)

$\begingroup$@crayon, yeah, except for the last one. incandescent bulbs aren't everywhere anymore (at least in the US). However, note that mercury vapor in compact fluorescent bulbs is also unfriendly, but in a different way :)$\endgroup$
– NH.Mar 8 '18 at 20:06

1

$\begingroup$Ok I enjoyed this but feel somewhat dissatisfied with the unfriendly air bit. Unfriendly gas would have been more entertaining and more accurate. As it stands the air aspect of the clue is slightly distracting and my gut says it doesn't quite sit. Am I being pedantic?$\endgroup$
– SentinelMar 8 '18 at 22:26

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$\begingroup$I agree that the “air” bit is a little far-fetched. To your point, I also think the “touch the stem” part is kinda out there, too. If I’m touching the stem, it must mean that the cap is off and the gas has already escaped. But that’s my interpretation—it would appear that OP is from India and English may not be their first language. I believe the key to solving (and, might I add, enjoying) any puzzle is to understand the intent of the author. Some grace may be required. :)$\endgroup$
– The SpartanMar 8 '18 at 23:29

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$\begingroup$Re the air bit, if you want to debate fully, by the time the gas has been dispersed and reached you ("you will meet") it has mixed with air and the mixture is possibly a higher percentage air than the gas released. Had the clue instead specified (e.g.) "bad air will be released" then it would have been misleading. As "you will meet" is open to vast interpretation I think it's fine in the specific context. I even at one point analysed the potential specifics of "meet". Great puzzle though and well worked out!$\endgroup$
– JamesMar 10 '18 at 13:04

$\begingroup$nopes, but thanks for teaching me about a new thing, i will check out the video:)$\endgroup$
– crayonMar 7 '18 at 16:58

2

$\begingroup$What a fascinating thing! Clever answer to the riddle... now I'm off to read more about these :)$\endgroup$
– puzzledPigMar 7 '18 at 17:40

$\begingroup$Strictly speaking, the head isn't bulletproof. It'll break if you hit it with a bullet. However, it's very difficult to hit it head-on, and it's great at making bullets ricochet off the sides, and you're much more likely to break it by accidentally twisting the tail.$\endgroup$
– Nic HartleyMar 8 '18 at 6:53

$\begingroup$Nice try,check out the new hint$\endgroup$
– crayonMar 8 '18 at 7:24

$\begingroup$Edited my answer-- wasn't sure what the best way to go about editing is, so I will strike out the previous attempted$\endgroup$
– MilkMar 8 '18 at 16:03

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$\begingroup$(Previous versions are always retained as part of the edit history - there's no need to retain the original, unless the original version is for some reason important to or referenced by the update. Feel free to clean up your answer to remove the original attempt.)$\endgroup$
– Rubio♦Mar 8 '18 at 17:21

$\begingroup$@Rubio Ah, thank you so much! I'm still very new around here :)$\endgroup$
– MilkMar 8 '18 at 18:36

$\begingroup$Everyone was new here once :)$\endgroup$
– Rubio♦Mar 8 '18 at 18:58

Mushrooms, or maybe specifically puffball mushrooms. They have caps and stems, are pretty fragile, come in many colors, and puffball mushrooms release spores and dust on contact with things such as raindrops.

Once lit the grease from your fingers will cause it to explode and release the halogen gas inside."Unfriendly" might be a play on words with Bromine as in "bro" (a friend) and "mine" (the explosive device).
Much more likely is that "unfriendly" refers to the inability of Noble gasses to form bonds. However, noble gasses are not halogens, and noble gas lamps (such as neon tubes) do not have any special handling AFAIK.

mushrooms fit both these - many varieties are fragile, and they can be a wide range of colors

You can touch my cap

generally, touching the top of a mushroom won't do you any harm

But if you touch my stem
Unfriendly air will you meet.

by touching the stem you can release spores (from the little frills underneath the cap - I've forgotten the exact terms). This can be "unfriendly air" because a) spores can be unpleasant/harmful to ingest and b) they create more mushrooms - not great if the mushrooms were unwanted/toxic!

you can touch the bulb itself but if you break the stem the mercury will release and mecury is generally not too good for you

EDIT

Compact fluorescents, like their tubular fluorescent precursors, contain a small amount of mercury—typically around five milligrams. Mercury is essential to a fluorescent bulb's ability to emit light; no other element has proved as efficient.

$\begingroup$Welcome to Puzzling.SE! Could you edit your answer to include spoiler tags, so as not to spoil your solution for anyone who wants to have a go at the puzzle themselves? Thanks!$\endgroup$
– F1KrazyMar 9 '18 at 15:53

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$\begingroup$Sorry, didn't see how to do that the first go. This should help.$\endgroup$
– Ray WellsMar 9 '18 at 17:33